A motor controller is roughly divided into two sections: one is a motor position detector for detecting a rotating position of the motor hereinafter referred to as “motor-position”), and the other is a motor driver. FIG. 24 shows a structure of conventional motor position detector 100 and its connection to motor driver 120. Power supplying circuit 121 disposed in motor driver 120 supplies a power line voltage to power receiving circuit 101 disposed in motor position detector 100 via power cable 118 comprising a pair of electric lines. Power receiving circuit 101 powers respective circuits disposed in motor position detector 100 via lines (not shown). Position detecting circuit 102 coupled to motor 90 detects a motor position, and outputs the parallel information about the motor position. Encoding circuit 103 converts the parallel information into serial information. Motor-position-transmitting circuit 104 outputs the serial information about the motor position in a differential manner to signal cable 119 comprising a pair of lines. Motor position receiving circuit 122 disposed in motor driver 120 receives this serial information about the motor position via signal cable 119. Decoding circuit 123 converts the serial information about the motor position into parallel information. Motor driving circuit 140 drives the motor based on the parallel information thus obtained.
FIG. 25 shows an entire structure of a conventional motor controller, and illustrates details of motor driving circuit 140—surrounded by a bold line—disposed in motor driver 120. Three functions are built in motor-driving circuit 140, namely, a position instructing function, a speed instructing function and a torque instructing function.
When the position instructing function is activated, position control circuit 124 controls a position with motor position information θ and outer position instruction s1, then outputs inner speed instruction s4. Speed control circuit 126 controls a speed with speed information θ′ and inner speed instruction s4. Speed information θ′ is obtained by differentiating motor-position information θ in differentiating circuit 125. Circuit 126 then outputs inner torque instruction s5. Current detecting circuit 127 detects motor current information s6. Torque control circuit 128 supplies a command to gate drive circuit 129 based on inner torque instruction s5 and motor position information θ, thereby controlling motor current running through power circuit 130.
When the speed instructing function is activated, a speed is controlled by speed control circuit 126 using speed information θ′ and outer speed instruction s2, and this control does not need position control circuit 124.
When the torque instructing function is activated, torque control circuit 128 controls motor current based on outer torque instruction s3 and motor position information θ. This control does not need both of position control circuit 124 and speed control circuit 126.
In the conventional motor controller discussed above, a power cable having one pair of lines (i.e., two lines) and a signal cable having one pair of lines (i.e., two lines) couple the motor position detector to the motor driver. In total two pairs of lines (i.e., four lines) are used. The present invention aims to provide a motor controller in which a motor position detector is coupled to a motor driver with only one pair of lines (i.e., two lines).